It is widely recognized that the function of a number of detergent additive materials can be significantly impaired in detergent compositions by interaction between the additive material and other components of the composition. For example, enzyme, perfumes, fluorescers and bleach activators can deleteriously interact with peroxy bleaches; since organic bleach activators are generally hydrolysable compounds, they tend to hydrolyse or perhydrolyse owing to the action of moisture, alkaline substances and the percompound present in the detergent composition. Also organic peroxyacid bleach compounds and chlorine bleach compounds, such as diperoxydodecanedioic acid and the chloroisocyanurates, when incorporated in detergent compositions tend to attack oxidation-sensitive ingredients such as perfumes, fluorescers and dyes. Cationic compounds can be deleteriously affected by interaction with anionic ingredients, e.g. anionic surfactants. Numerous attempts have been made to improve the storage-stability characteristics of detergent additive materials, such as bleach activators and the like, but such attempts have in general encountered only limited success. The most common way of approaching the problem has been to protect the additive material from its hostile environment by agglomerating, coating or encapsulating the material with a non-hygroscopic, preferably hydrophobic material. Conventionally, organic materials have found the greatest favour as coating/agglomerating agents because such materials readily form a substantially cohesive and continuous plastic matrix in which the additive material can be embedded. GB-A-1 204 123, GB-A-1,441,416 and GB-A-1,398,785 are representative of this general approach.
In general, these disclosures teach the incorporation of a fine particulate bleach activator (hereinafter also referred to as peroxyacid bleach precursor), optionally with additional stabilising compounds, into larger agglomerates, using organic solids having melting points in the range of 30-.degree.60.degree. C. as the agglomerating agents.
Unfortunately, however, protection of sensitive ingredients within an organic plastic matrix as practised in the art can have detrimental effect on the dispersibility or dissolution characteristics of the ingredient in water, particularly at low temperatures.
U.S. Pat. No. 4,009,113 discloses granular compositions comprising from about 40% to 80% of a bleach activator and a non-hygroscopic carrier material such as paraffins and certain long-chain fatty acid or ester wherein said precursor is substantially evenly distributed in the bulk forming a composite particle. The particle has an outer protective layer which can consist of, for example, polyvinyl alcohol. The particles according to this patent can be made in a one-step process using a machine termed a "Marumeriser".RTM. by Fuji Paudal KK, or in a two-step process wherein the precursor/carrier mixture is processed by extrusion to form extrudates, which are then broken down in a "Marumeriser" and formed into spheres and coating the spherical particles. It is stated that such compositions have both good storage stability and dispersibility in the wash water.
U.S. Pat. No. 4,399,049 (=EP-A-0062523) discloses a detergent additive composition comprising from 75% to 95% (84-90%) of a particulate solid (e.g. bleach activator) having a particle size distribution such that at least about 50% thereof passes a 250 micrometer screen, and from 5% to 25% (10-16%) of ethoxylated nonionic surfactant melting in the range of from 20.degree. C. to 60.degree. C., wherein said composition is prepared via a radial extrusion process. It is stated that such compositions have improved storage stability together with excellent release and dispersibility characteristics in wash water.
EP-A-0106634 discloses activator-containing bodies comprising a bleach activator and an organic binder material having a melting point not below 40.degree. C., wherein the bleach activator and binder material are evenly distributed throughout the body such that the body has the proper density, prepared via compaction pressing or a radial extrusion process. It is stated that such bodies have both superior storage stability and dispersibility in the wash water.
Still, in all of these prior art disclosures the primary objective has been the formation of a bleach additive granule containing a peroxy bleach activator whose chemical stability could be maintained in a hostile environment, e.g. during storage under conditions of elevated temperature and humidity in intimate contact with an alkaline peroxy bleach-containing detergent. Indeed, since bleach activators, i.e. peroxyacid bleach precursors, are reactive compounds which function by the generation of peroxyacids in alkaline solutions containing a source of hydrogen peroxide, such as sodium perborate, a reaction which is often referred to as perhydrolysis, it is essential that detergent additive particles comprising a bleach activator should disperse well and dissolve rapidly into the wash liquor to obtain maximum benefit from their use. Other detergent additive materials will also benefit from these properties.
However, it is also very desirable that the detergent additive material, particularly the highly reactive peroxyacid bleach precursors and chlorinated or peroxyacid bleach compounds, be formed into granulated particles or granules, which have sufficient mechanical strength and attrition resistance to allow them to be stored and conveyed safely by bulk handling methods. The more aggressive the detergent additive material, the more important this criterion will be.
In the case of peroxyacid bleach and/or its precursors it was known how to meet the first criterion. It may also be known how to meet the second criterion, but this has hitherto been at the expense of the requirements set out for really good dispersibility and rapid dissolution of the particles.